Devices which digitally record and play back TV programs, known as PVRs (Personal Video Recorders), are well known and widely available. One example of a PVR is the XTV™ system, commercially available from NDS Limited, One Heathrow Boulevard, 286 Bath Road, West Drayton, Middlesex UB7 0BQ, United Kingdom. Another example of such a system is manufactured by Tivo Inc., 2160 Gold Street, Alviso, Calif. 95002-2160, USA.
PVRs are also known as Digital Video Recorders (DVRs). The term “PVR”, in all its grammatical forms, is used throughout the present specification and claims interchangeably with the term “DVR” and its corresponding grammatical forms.
PVRs are described in the following patents and patent applications, the disclosures of which are hereby incorporated herein by reference: PCT Published Patent Application WO 00/01149 of NDS Limited; corresponding European Patent 1 013 088 to NDS Limited; and U.S. patent application Ser. No. 09/515,118 of Wachtfogel et al, assigned to NDS Limited.
TV programs often have breaks for commercial advertisements inserted into the program flow. Broadcasters have an interest in having viewers watch the commercial advertisements, as they are a source for the broadcasters' income. Television viewers are often impatient with commercial advertisements, and when a program is played back from a recording, viewers fast-forward through the commercial advertisement break, thus “skipping” the commercial advertisement break.
Skipping commercial advertisements is easy when using PVRs. In fact, some PVRs support the skipping by providing a specific PVR playback function which enables skipping 30 seconds of programming, which is especially useful for skipping a typical commercial advertisement.
The following references are believed to represent the state of the art:
U.S. Pat. No. 6,654,547 to Maeda et al;
US Published Patent Application 2004/0028226 of Saar et al;
PCT Published Patent Application WO 00/01149 of NDS Ltd, corresponding European Patent 1 013 088 of NDS Ltd., and corresponding U.S. patent application Ser. No. 09/515,118 of Wachtfogel et al;
SHA-1, Secure Hash Standard, described in FIPS 180-1 (Federal Information Processing Standards Publication 180-1), found on the World Wide Web at www.itl.nist.gov/fipspubs/fip180-1.htm;
AES described in FIPS 197 (Federal Information Processing Standards Publication 197), found on the World Wide Web at csrc.nist.gov/publications/fips/fips197/fips-197.pdf;
DES described in FIPS 46-3 (Federal Information Processing Standards Publication 46-3), found on the World Wide Web at csrc.nist.gov/publications/fips/fips46-3/fips46-3.pdf; and
DVB-CSA described in ETSI Technical Report ETR 289, of October 1996, published by the European Telecommunications Standards Institute.
The disclosures of all references mentioned above and throughout the present specification, as well as the disclosures of all references mentioned in those references, are hereby incorporated herein by reference.